Generally speaking a 3.3 and a 2.5 are both going to be small block engines so they should be swappable. Just make sure the carb type and exhaust port match.
As for the metal spur, the whole idea behind using plastic spurs and a-arms is because these are selective failure points. Meaning, if you have an unseen issue or a wreck, you will be more likely to break those cheap and easy to replace parts instead of something more expensive and harder to replace. In the case of arms you also have to take into account that a-arms take a lot of abuse is wrecks and aluminum arms won't give so while they may be stronger and hold up fine for smaller wrecks the nastier wrecks you will eventually bend those arms, and you won't be able to straighten them. Also, the metal arms will transfer much more energy in to bulkheads, shock towers etc. causing more damage to them as well. As for the spur, let's say you're running a plastic spur, which will generally hold up just fine given no other issues are present in the drive line. If you develop an issue in your drive line, like a couple of partially seized bearings, then that will cause the spur to heat up and melt. A cheap and easy fix. If you're running a metal spur and that happens, then you keep running until something inside the tranny or drive line grenades. Much more expensive and time-consuming to fix now. Hope this helps.